Voltage-controlled semiconductor inductor and method

ABSTRACT

A voltage-controlled semiconductor inductor and method is provided. According to various embodiments, the voltage-controlled inductor includes a conductor configured with a number of inductive coils. The inductor also includes a semiconductor material having a contact with at least a portion of at least one of the coils. The semiconductor material is doped to form a diode with a first doped region of first conductivity type, a second doped region of second conductivity type, and a depletion region. A voltage across the diode changes lengths of the first doped region, the second doped region and the depletion region, and adjacent coils in contact with at least one of the doped regions are electrically shorted, thereby varying the inductance of the inductor. In various embodiments, the inductor is electrically connected to a resistor and a capacitor to provide a tunable RLC circuit. Other aspects and embodiments are provided herein.

TECHNICAL FIELD

This disclosure relates to electrical circuits, and more particularly,to variable inductors.

BACKGROUND

Some electronic devices use tuning circuits in their operation. Examplesinclude radio receivers and cellular telephones. Common tuning circuitsinclude RLC (resistor-inductor-capacitor) circuits which use a variablecapacitor to “tune” the circuit over a range of frequencies. In thesevariable-capacitor RLC circuits, the range of frequencies is limited bythe range of capacitance over which a variable capacitor may beadjusted.

SUMMARY

The above-mentioned problems and others not expressly discussed hereinare addressed by the present subject matter and will be understood byreading and studying this specification.

Disclosed herein, among other things, is a voltage-controlled inductor.According to various embodiments, the inductor includes a conductorconfigured with a number of inductive coils. The inductor also includesa semiconductor material having a contact with at least a portion of atleast one of the coils. The semiconductor material is doped to form adiode with a first doped region of first conductivity type, a seconddoped region of second conductivity type different from the firstconductivity type, and a depletion region. A voltage across the diodechanges lengths of the first doped region, the second doped region andthe depletion region, and adjacent coils in contact with at least one ofthe doped regions are electrically shorted, thereby varying theinductance of the inductor.

One aspect of this disclosure relates to an apparatus with avoltage-controlled inductor. According to an embodiment, the apparatusincludes a resistor, a capacitor electrically connected to the resistor,and a voltage-controlled variable inductor electrically connected to theresistor and the capacitor, where inductance of the inductor is variedto change the resonant frequency of the apparatus. According to oneembodiment, the capacitor includes a variable capacitance. According tovarious embodiments, the inductor includes a conductor configured with anumber of inductive turns, and at least one diode electrically connectedwith at least a portion of at least one of the turns. A voltage acrossthe at least one diode changes the dimensions of a depletion region, afirst doped terminal region and a second doped terminal region, andadjacent turns in contact with at least one of the doped terminalregions are electrically shorted, thereby varying the inductance of theinductor.

According to various embodiments, an apparatus includes a resistor, acapacitor electrically connected to the resistor, and a variableinductor electrically connected to the resistor and the capacitor. Thevariable inductor includes a conductor configured with a number ofinductive coils, and a semiconductor material having an ohmic contactwith at least a portion of at least one of the coils. The semiconductormaterial is doped to form a diode with a first doped region of firstconductivity type, a second doped region of second conductivity typedifferent from the first conductivity type, and a depletion region. Avoltage across the diode changes lengths of the first doped region, thesecond doped region and the depletion region, and adjacent coils incontact with at least one of the doped regions are electrically shorted,thereby varying the inductance of the inductor.

One aspect of this disclosure relates to a method of operating avariable inductor with a number of turns and a diode in contact with atleast two of the number of turns. According to various embodiments, themethod includes applying a first voltage across the diode to provide alength of a depletion region, a first diode terminal region, and asecond diode terminal region of the diode to short a first number ofturns to provide a first inductance for the variable inductor. Themethod also includes applying a second voltage across the diode tochange the length of the depletion region, the first diode terminalregion and the second diode terminal region of the diode to short asecond number of turns to provide a second inductance for the variableinductor.

One aspect of this disclosure relates to a method for making a variableinductor. According to various embodiments, the method includes forminga semiconductor material having an ohmic contact with at least a portionof a number of inductor coils. The method also includes doping thesemiconductor material to form a diode such that a predetermined voltageapplied across the diode electrically shorts a predetermined number ofadjacent coils. According to an embodiment, doping the semiconductormaterial includes forming a plurality of diodes.

This Summary is an overview of some of the teachings of the presentapplication and is not intended to be an exclusive or exhaustivetreatment of the present subject matter. Further details are found inthe detailed description and appended claims. Other aspects will beapparent to persons skilled in the art upon reading and understandingthe following detailed description and viewing the drawings that form apart thereof, each of which is not to be taken in a limiting sense. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an isometric view of a voltage-controlled inductor,according to various embodiments.

FIG. 2A illustrates a side view of a voltage-controlled inductor,according to various embodiments.

FIG. 2B illustrates a voltage-controlled inductor with multiple diodes,according to various embodiments.

FIG. 3 illustrates a voltage-controlled inductor with helical turns,according to various embodiments.

FIG. 4 illustrates a variable inductor, according to variousembodiments.

FIG. 5 illustrates a voltage-controlled inductor, according to variousembodiments.

FIG. 6 illustrates a flow diagram of a method of operating a variableinductor, according to various embodiments.

FIG. 7 illustrates a flow diagram of a method for making a variableinductor, according to various embodiments.

FIGS. 8A-8F illustrate a series of diagrams depicting a method formaking a variable inductor, according to various embodiments.

FIG. 9A illustrates a series RLC circuit using a voltage-controlledinductor, according to various embodiments.

FIG. 9B illustrates a parallel RLC circuit using a voltage-controlledinductor, according to various embodiments.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawingswhich show, by way of illustration, specific aspects and embodiments inwhich the present invention may be practiced. The various embodimentsare not necessarily mutually exclusive, as aspects of one embodiment canbe combined with aspects of another embodiment. These embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the invention. Other embodiments may be utilized andstructural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention.

Some electronic devices use tuning circuits in their operation. Examplesinclude radio receivers and cellular telephones. Common tuning circuitsinclude RLC (resistor-inductor-capacitor) circuits which use a variablecapacitor to “tune” the circuit over a range of frequencies. In thesevariable-capacitor RLC circuits, the range of frequencies is limited bythe range of capacitance over which a variable capacitor may beadjusted. Disclosed herein is a variable inductor that can be used witha variable capacitor to increase the range of frequencies for an RLCtuning circuit. The variable inductor provided by the present subjectmatter is easily adjustable over a range of inductance and is capable ofmanufacture by common semiconductor fabrication techniques.

Voltage-Controlled Inductor

FIG. 1 illustrates an isometric view of a voltage-controlled inductor,according to various embodiments. According to an embodiment, theinductor 100 includes a conductor 104 configured with a number ofinductive coils. The inductor also includes a semiconductor material 102having a contact with at least a portion of at least one of the coils.In an embodiment, the semiconductor material has an ohmic contact withat least a portion of at least one of the coils. The semiconductormaterial can have a Shottky contact with at least a portion of at leastone of the coils, in an embodiment. In general two types of contacts aremade to a semiconductor, the ohmic contact and the Shottky or rectifyingcontact. An ohmic contact refers to a metal-semiconductor contact withvery low resistance independent of applied voltage. To form an ohmiccontact, the metal and semiconductor are selected such that there is nopotential barrier formed at the interface (or potential barrier is sothin that charge carriers can readily tunnel through it). A Shottkycontact refers to a metal-semiconductor contact displaying asymmetriccurrent-voltage characteristics, allowing high current to flow acrossunder the forward bias condition and blocking current under the reversebias. This behavior is controlled by the bias voltage dependent changesof the potential barrier height in the contact region. The work functionof the conductor and the semiconductor determine whether a contact onthe semiconductor will have ohmic or rectifying properties. Variousembodiments of the present disclosure use the properties of the ohmiccontact, by doping the semiconductor to an appropriate level, althoughShottky contacts may also be used.

FIG. 2A illustrates a side view of a voltage-controlled inductor,according to various embodiments. According to an embodiment, theinductor 200 includes a conductor 204 configured with a number ofinductive coils 205. The inductor also includes a semiconductor material202 having an ohmic contact 206 with at least a portion of at least oneof the coils, where the semiconductor material is doped to form a diodewith a first doped region of first conductivity type 208, a second dopedregion of second conductivity type different from the first conductivitytype 210, and a depletion region 212. A voltage across the diode changeslengths of the first doped region, the second doped region and thedepletion region, and adjacent coils in contact with at least one of thedoped regions are electrically shorted, thereby varying the inductanceof the inductor. A single coil or turn begins at a contact point withthe diode and ends at an adjacent contact point with the diode. As thereverse bias is varied across the diode, the depletion region sizeincreases or decreases. Since the depletion region is substantiallyequivalent to an insulator due to the lack of carriers, the coils orturns passing through the depletion region remain isolated. However,coils or turns passing through the first doped region (p-doped region inFIG. 2A) or the second doped region (n-doped region in FIG. 2A) of thediode will be shorted because of the availability of carriers. In FIG.2A, coils A, B, G, and H are outside the depletion region andelectrically shorted, while coils C, D, E, and F are in contact with thedepletion region and remain part of the inductor. In an embodiment, theapparatus further includes a magnetic core within the coils.

FIG. 2B illustrates a voltage-controlled inductor 250 with multiplediodes, according to various embodiments. In applications requiringlarge variations in voltage-controlled inductance, several diodes may beused to short or isolate various turns in a single long inductor. InFIG. 2B, two diodes, 252 and 254, are used to vary the inductance ofinductor 250. The first diode 252 has a p-doped region 261, an n-dopedregion 263, and a depletion region 262 under reverse bias. The seconddiode 254 has a p-doped region 271, an n-doped region 273, and adepletion region 272 under reverse bias. In the depicted embodiment,turns B, G, and H remain part of the inductor as they are in contactwith a depletion region. In an embodiment, three diodes are used. Inanother embodiment, four diodes are used. In a further embodiment, Ndiodes are used. Those of skill in the art will recognize that furtherembodiments with more diodes are within the scope of this disclosure. Invarious embodiments, each of the diodes is adapted to have an ohmiccontact with at least a portion of at least one of the coils.

FIG. 3 illustrates a voltage-controlled inductor with helical turns,according to various embodiments. According to an embodiment, theinductor 300 includes a conductor 304 configured with a number ofhelical inductive coils 305. The inductor also includes a semiconductormaterial 302 having an ohmic contact with at least a portion of at leastone of the coils, where the semiconductor material is doped to form adiode with a first diode terminal region 308, a second diode terminalregion 310 and a depletion region 312. A voltage across the diodechanges the dimensions of the first terminal region, the second terminalregion and the depletion region, and adjacent coils in contact with atleast one of the terminal regions are electrically shorted, therebyvarying the inductance of the inductor. A single coil begins at acontact point with the diode and ends at an adjacent contact point withthe diode. As the reverse bias is varied across the diode, the depletionregion size would increase or decrease. In FIG. 3, coils A, B, E, and Fare outside the depletion region and electrically shorted, while coils Cand D are in contact with the depletion region and remain part of theinductor.

FIG. 4 illustrates a variable inductor, according to variousembodiments. According to an embodiment, the inductor 400 includes aconductor 404 configured with a number of inductive turns 405. Theinductor also includes a semiconductor material 402 having an ohmiccontact with at least a portion of at least one of the turns, where thesemiconductor material is doped to form a diode with a first dopedregion having a first conductivity type 408, a second doped regionhaving a second conductivity type different from the first conductivitytype 410, and a depletion region 412. A voltage across the diode changesthe dimensions of the first doped region, the second doped region andthe depletion region, and adjacent coils in contact with at least one ofthe doped regions are electrically shorted, thereby varying theinductance of the inductor. A single turn begins at a contact point withthe diode and ends at an adjacent contact point with the diode. As thereverse bias is varied across the diode, the depletion region size wouldincrease or decrease. In FIG. 4, coils C, D, E, and F are outside thedepletion region and electrically shorted, while coils A and B are incontact with the depletion region and remain part of the inductor. Thedepicted embodiment has inductor turns contacting only the n-dopedregion and depletion region. No turns are contacting the p-doped region.

FIG. 5 illustrates a voltage-controlled inductor, according to variousembodiments. According to an embodiment, the inductor 500 includes aconductor 504 configured with a number of inductive turns 505. Theinductor also includes a semiconductor material 502 having an ohmiccontact with at least a portion of at least one of the turns, where thesemiconductor material is doped to form a diode with a first dopedregion of first conductivity type 508, a second doped region of secondconductivity type different from the first conductivity type 510, and adepletion region 512. A voltage across the diode changes the dimensionsof the first doped region, the second doped region and the depletionregion, and adjacent coils in contact with at least one of the dopedregions are electrically shorted, thereby varying the inductance of theinductor. A single turn begins at a contact point with the diode andends at an adjacent contact point with the diode. As the reverse bias isvaried across the diode, the depletion region size would increase ordecrease. In FIG. 5, coils A, B, and C are outside the depletion regionand electrically shorted, while coil D is in contact with the depletionregion and remains part of the inductor. The depicted embodiment hasinductor turns contacting only the p-doped region, and depletion region.No turns are contacting the n-doped region.

Method of Operating a Variable Inductor

FIG. 6 illustrates a flow diagram of a method of operating a variableinductor, according to various embodiments. One aspect of thisdisclosure relates to method 600 of operating a variable inductor with anumber of turns and a diode in contact with at least a portion of atleast one of the number of turns. According to various embodiments, themethod includes applying a first voltage across the diode to provide alength of a depletion region, a first diode terminal region, and asecond diode terminal region of the diode to short a first number ofturns to provide a first inductance for the variable inductor, at 602.The method also includes applying a second voltage across the diode tochange the length of the depletion region, the first diode terminalregion and the second diode terminal region of the diode to short asecond number of turns to provide a second inductance for the variableinductor, at 604.

The total number of turns that may be shorted is controlled by varyingthe reverse bias voltage. As a result of this interplay of connectionand isolation of several turns within an inductor, the overallinductance of a device can be varied. This variation in inductance is indiscrete steps, with the step size being the inductance generated by asingle turn.

According to an embodiment, applying the first voltage electricallyshorts zero adjacent turns to provide a first inductance for thevariable inductor. Applying the second voltage electrically shorts zeroadjacent turns to provide a second inductance for the variable inductor,according to an embodiment. In one embodiment, applying the secondvoltage provides the second number of turns less than the first numberof turns. Applying the second voltage provides the second number ofturns equal to the first number of turns, in an embodiment.

Method for Making a Variable Inductor

FIG. 7 illustrates a flow diagram of a method for making a variableinductor, according to various embodiments. According to variousembodiments, the method 700 includes forming a semiconductor materialhaving an ohmic contact with at least a portion of a number of inductorcoils, at 702. The method also includes doping the semiconductormaterial to form a diode such that such that a predetermined voltageapplied across the diode electrically shorts a predetermined number ofadjacent coils, at 704. According to an embodiment, doping thesemiconductor material includes forming a plurality of diodes. In anembodiment, lower doping levels are used to enable wider depletionregions at lower reverse bias voltage levels. In various embodiments,doping levels of 1e¹⁵ to 1e¹⁸ per cm³ are used, with or without dopinggradients that can be generated using implantation.

According to various embodiments, applying a reverse bias voltage acrossthe diode increases a dimension of a depletion region of the diode andincreases the number of inductor coils in contact with the depletionregion, thereby varying the inductance of the inductor. Applying avoltage across the diode changes a dimension of a p-doped region of thediode and changes the number of inductor coils in contact with thep-doped region, thereby varying the inductance of the inductor in anembodiment. According to an embodiment, applying a voltage across thediode changes a dimension of an n-doped region of the diode and changesthe number of inductor coils in contact with the n-doped region, therebyvarying the inductance of the inductor.

FIGS. 8A-8F illustrate a series of diagrams depicting a method formaking a variable inductor, according to various embodiments. Ohmiccontact material is used to build inductor coils, and square shapedcoils are used in the variable inductor in the depicted embodiment. FIG.8A illustrates a single square shaped coil 800 with sides (or wires)labeled A, B, C, and D. One of skill in the art will recognize thatother conductor shapes, such as helical or elongated coils for example,can be used with the semiconductor diode to provide a voltage-controlledinductor.

According to various embodiments, steps for making a variable inductorinclude laying down on a substrate the side of the coil labeled C asshown in FIG. 8B. The illustrated C lines are generally parallel to eachother and horizontal with respect to the substrate. In FIG. 8C, wireslabeled B and D are subsequently deposited on the substrate. Theillustrated B and D lines are generally parallel to each other andvertical with respect to the substrate. In FIG. 8D, a trench feature isetched in the substrate to deposit a semiconductor material 802. Invarious embodiments, the depth of the trench is such that the wires arecompletely immersed in the semiconductor material. In an embodiment, thedepth of the trench is several times the thickness of the inductorwire's diameter. In FIG. 8E, the connecting wires labeled A are laid ontop of the semiconductor material in an embodiment. Subsequently in FIG.8F, additional semiconductor material 804 is laid over the previouslydeposited material 802. The wires A are effectively sandwiched betweentwo layers of semiconductor material in this embodiment. Finally,appropriate doping is performed to convert the semiconductor materialinto a p-n or n-p diode, in various embodiments.

According to an embodiment, the method for making a variable inductorincludes forming a series of lower conductors of equal length on asubstrate using ohmic contact forming material, each of the lowerconductors parallel to one another and having a first end and a secondend. The method also includes forming a series of first uprightconductors and a series of second upright conductors in the substratevertically from the series of lower conductors using ohmic contactforming material. The first upright conductors have a lower end and anupper end, the lower end connecting to first end of the lowerconductors, and the second upright conductors having a lower end and anupper end, the lower end connecting to the second end of the lowerconductors at right angles to the lower conductors. The method furtherincludes etching a trench in the substrate. The trench has a depthgreater than a thickness of the connecting conductor but less than alength of the upright conductors, and a width less than a length of thelower conductors. A first layer of semiconductor material is depositedto fill in the trench. According to an embodiment, the method alsoincludes forming a series of connecting conductors along the top of thesemiconductor material. Each of the connecting conductors is parallel toeach other, with one end of each connecting conductor contacting theupper end of a first upright conductor, and further contacting the upperend of a second upright conductor whose lower end is connected to anadjacent lower conductor. The method also includes depositing a secondlayer of semiconductor material upon the first layer of semiconductormaterial to sandwich the series of connecting conductors, and doping thefirst and second layer of semiconductor material to form a diodeperpendicular to the series of connecting conductors.

According to various embodiments, the diode can be formed on the bottomof the coils. The diode can be formed on a side of the coils, in anembodiment. Other methods of making the variable inductor are within thescope of this disclosure.

Applications Using a Variable Inductor

The present apparatus has a number of potential applications. Thefollowing examples, while not exhaustive, are illustrative of theseapplications.

An RLC circuit is a kind of electrical circuit composed of a resistor(R), an inductor (L), and a capacitor (C). A voltage source (V) is alsoimplied. It is called a second-order circuit or second-order filter asany voltage or current in the circuit is the solution to a second-orderdifferential equation. The RLC circuit is an example of an electricalharmonic oscillator. The resonant or center frequency of such a circuit(in hertz) is:f _(c)=1/2π√(LC)It is a form of bandpass or bandcut filter, and the Q factor is:Q=f _(c) /BW=2πf _(c) /R=1/√(R ² C/L)There are two common configurations of RLC circuits: series (shown inFIG. 9A) and parallel (shown in FIG. 9B).

FIG. 9A illustrates a series RLC circuit using a voltage-controlledinductor, according to various embodiments. One aspect of thisdisclosure relates to an apparatus with a voltage-controlled inductor.According to an embodiment, the apparatus includes a resistor R, acapacitor C electrically connected to the resistor, and avoltage-controlled variable inductor L electrically connected to theresistor and the capacitor, where inductance of the inductor is variedto change the resonant frequency of the apparatus. According to variousembodiments, the variable inductor L includes inductors described inFIGS. 1-5 described above. According to one embodiment, the capacitor Cincludes a variable capacitor.

FIG. 9B illustrates a parallel RLC circuit using a voltage-controlledinductor, according to various embodiments. One aspect of thisdisclosure relates to an apparatus with a voltage-controlled inductor.According to an embodiment, the apparatus includes a resistor R, acapacitor C electrically connected to the resistor, and avoltage-controlled variable inductor L electrically connected to theresistor and the capacitor, where inductance of the inductor is variedto change the resonant frequency of the apparatus. According to variousembodiments, the variable inductor L includes inductors described inFIGS. 1-5 above. According to one embodiment, the capacitor C includes avariable capacitance.

In an electrical circuit, resonance occurs at a particular frequencywhen the inductive reactance and the capacitive reactance are of equalmagnitude, causing electrical energy to oscillate between the magneticfield of the inductor and the electrical field of the capacitor.Resonance occurs because the collapsing magnetic field of the inductorgenerates an electric current in its windings that charges thecapacitor, and the discharging capacitor provides an electric currentthat builds the magnetic field in the inductor, and the process isrepeated. An analogy is a mechanical pendulum. At resonance, the seriesimpedance of the two elements is at a minimum and the parallel impedanceis at a maximum. Resonance is used for tuning and filtering, becauseresonance occurs at a particular frequency for given values ofcapacitance and inductance.

An example of an RLC circuit is a radio tuner. The antenna of the radiopicks up radio signals from every station in the area, but only thestation whose frequency matches the natural (resonant) frequency of thetuning circuit will cause large currents to flow in the circuit. Thesecurrents, when amplified, are the ones that produce the sound heard by alistener. If the circuit is not properly tuned, then it may pick up twostations equally well.

In various embodiments of the apparatus described in FIGS. 9A and 9B,the resistor, capacitor and variable inductor are adapted for tuning acellular telephone receiver. In other embodiments, the resistor,capacitor and variable inductor are adapted for tuning a radio receiver.In further embodiments, the resistor, capacitor and variable inductorare adapted for tuning a satellite receiver. In various embodiments, theapparatus described is adapted for use in timing for memory circuits, toadjust a high frequency response.

FIGS. 9A and 9B are examples of RLC circuits. More complex circuits canhave resistors, capacitors and variable inductors and have a resonantfrequency. Other applications for variable inductors include use in highspeed global interconnect circuit designs, which provide on-chiptransmission lines for global signaling at the velocity of light. Suchcircuits require precise inductances and will not properly operate ifmismatched. In an embodiment, the disclosed variable inductor provides aconvenient way of ensuring matching components in the described highspeed global interconnect circuits.

Further applications for variable inductors include use in matchingcircuits for radio frequency (RF) plasma processing tools. Matchingcircuits utilizing the disclosed variable inductor can provide morerapid matching compared to conventional stepper motor controlledmatching circuits. Such quick response matching circuits are well suitedfor plasma-enhanced atomic layer deposition (PEALD) processes, whereplasma is cycled on and off frequently.

This disclosure includes several processes, diagrams, and structures.The present invention is not limited to a particular process order orlogical arrangement. Although specific embodiments have been illustratedand described herein, it will be appreciated by those of ordinary skillin the art that any arrangement which is calculated to achieve the samepurpose may be substituted for the specific embodiment shown. Thisapplication is intended to cover adaptations or variations, and includesany other applications in which the above structures and fabricationmethods are used. It is to be understood that the above description isintended to be illustrative, and not restrictive. Combinations of theabove embodiments, and other embodiments, will be apparent to those ofskill in the art upon reviewing the above description. The scope of thepresent invention should be determined with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

1. An apparatus, comprising: a resistor; a capacitor electrically connected to the resistor; and a voltage-controlled variable inductor electrically connected to the resistor and the capacitor, the inductor including: a conductor configured with a number of inductive turns; and at least one diode electrically connected with at least a portion of at least one of the turns; wherein inductance of the inductor is varied to change the resonant frequency of the apparatus.
 2. The apparatus of claim 1, wherein the capacitor includes a variable capacitance.
 3. The apparatus of claim 1, wherein a voltage across the at least one diode changes lengths of a depletion region, a first doped terminal region and a second doped terminal region, and wherein adjacent turns in contact with at least one of the doped terminal regions are electrically shorted, thereby varying the inductance of the inductor.
 4. The apparatus of claim 1, wherein the resistor, capacitor and variable inductor are adapted for tuning a cellular telephone receiver.
 5. The apparatus of claim 1, wherein the resistor, capacitor and variable inductor are adapted for tuning a radio receiver.
 6. An apparatus, comprising: a resistor; a capacitor electrically connected to the resistor; and a variable inductor electrically connected to the resistor and the capacitor, the variable inductor including: a conductor configured with a number of inductive coils; and a semiconductor material having an ohmic contact with at least a portion of at least one of the coils; wherein the semiconductor material is doped to form a diode with a first doped region of first conductivity type, a second doped region of second conductivity type different from the first conductivity type, and a depletion region, wherein a voltage across the diode changes lengths of the first doped region, the second doped region and the depletion region, and wherein adjacent coils in contact with at least one of the doped regions are electrically shorted, thereby varying the inductance of the inductor.
 7. The apparatus of claim 6, wherein the capacitor includes a variable capacitance.
 8. The apparatus of claim 6, wherein the resistor, capacitor and variable inductor are adapted for tuning a cellular telephone receiver.
 9. The apparatus of claim 6, wherein the resistor, capacitor and variable inductor are adapted for tuning a radio receiver.
 10. The apparatus of claim 6, wherein the resistor, capacitor and variable inductor are adapted for tuning a satellite receiver.
 11. An apparatus, comprising: a resistor; a capacitor electrically connected to the resistor; a voltage-controlled variable inductor electrically connected to the resistor and the capacitor; wherein inductance of the inductor is varied to change the resonant frequency of the apparatus; and wherein the inductor includes at least one semiconductor material including at least one diode.
 12. The apparatus of claim 11, wherein the capacitor includes a variable capacitance.
 13. The apparatus of claim 11, wherein the inductor includes a helical coil having an ohmic contact with the semiconductor material.
 14. The apparatus of claim 11, wherein the inductor includes a square coil having an ohmic contact with the semiconductor material.
 15. The apparatus of claim 11, wherein the inductor includes an irregularly-shaped coil having an ohmic contact with the semiconductor material.
 16. An apparatus, comprising: a resistor; a capacitor electrically connected to the resistor; and a variable inductor electrically connected to the resistor and the capacitor, the variable inductor including: a conductor configured with a number of helical inductive coils; and a semiconductor material having an ohmic contact with at least a portion of at least one of the coils; wherein the semiconductor material is doped to form a diode with a first doped region of first conductivity type, a second doped region of second conductivity type different from the first conductivity type, and a depletion region, wherein a voltage across the diode changes lengths of the first doped region, the second doped region and the depletion region, and wherein adjacent coils in contact with at least one of the doped regions are electrically shorted, thereby varying the inductance of the inductor.
 17. The apparatus of claim 16, wherein the capacitor includes a variable capacitance.
 18. The apparatus of claim 16, wherein the semiconductor material is doped to form a plurality of diodes.
 19. The apparatus of claim 16, wherein the inductor, the resistor and the capacitor provide a tunable RLC circuit.
 20. The apparatus of claim 19, wherein tunable RLC circuit is adapted for tuning a wireless receiver. 